Yes the ck-1's and busman's have the same thread and are interchangable....however according to the link below, these bk caps are NOT interchangable with the ck-1's, so I suspect the idea would be that these would not work on the busman's either, though he would know better than I.
http://www.proaudiosolutions.com/product-p/avant-bk22.htmThis link:
http://recordinghacks.com/microphones/Avant/BK-2 Claims that there was a 2009 prototype that was transformerless, with all the goodies shown in the pic in the first post...apparently that was revised and the 2010 version now has an output transformer, no pad, no hpf, and also eliminated the Figure 8 cap....
Avantone's website seems to confirm this by stating that the bk 2.2 set includes 10 caps, not the 12 as originally shown and also stated in the proaudiosolutions link...